The present invention is directed toward the art of brazing, and more particularly, to a method for direct application of a brazing flux to a brazing surface.
Brazing is a process that involves the joining of components with a brazing filler material whose melting point is lower than that of either of the components. The brazing process is typically used to join components that are either metals or alloys. Typically, the brazing filler material is placed adjacent to or in between the two components to be joined and the assembly is then heated to a temperature where the brazing filler material melts but not the components. Upon cooling, the brazing filler material forms a metallurgical bond between the two surfaces of the components. Often, the surfaces to be joined include surface metal oxide layers that can prevent formation of a good brazing joint between the surfaces. Therefore, it is typical to include a brazing flux material in addition to the brazing filler material. Typical brazing fluxes contain either chlorides and/or fluorides and the flux material typically melts at a lower temperature than the brazing filler material. Once molten, the brazing flux material works to dissolve the hard shell of metal oxides on the two surfaces, which enhances the wetting and flow of the molten brazing filler material, thereby allowing it to be drawn freely by capillary force between the joints of the components to be brazed. The composition of the brazing filler material is determined by the composition of the surfaces to be joined as is known by those of ordinary skill in the art. Likewise, there are numerous brazing flux materials that are available and the particular one utilized depends on the identity of the components to be brazed. Typically, when brazing aluminum components the industry utilizes the flux, NOCOLOCK(copyright) manufactured by Solvay Fluor. This flux comprises a mixture of potassium fluoraluminates.
In current manufacturing processes, application of the brazing flux to the brazing surface prior to brazing of the apparatus is a difficult process. Typically, the brazing filler material is applied to one of the surfaces to be joined and the apparatus is pre-assembled. After pre-assembly the entire apparatus is often dipped in a water-flux slurry or such a water-flux slurry is sprayed onto the entire assembly. Alternatively, the flux material is applied on the entire apparatus via a static dry powder process. As discussed above, the flux is actually only required at the localized areas where the two surfaces are being joined. The entire fluxed apparatus is then passed into a brazing furnace where the brazing flux material becomes a liquid and tends to drip from the apparatus forming very hard residues inside the brazing furnace, which requires the furnace to be shut down and cleaned periodically. In addition, the heated brazing flux material generates fumes that must be treated prior to release into the atmosphere. Often brazing fluxes will not adhere well to a brazing surface and thus one is required to include additional binders and resins in order to adhere the brazing flux material to the brazing surface. Finally, these processes are wasteful because of the excess flux material that must be used.
It would be advantageous to provide a method for direct application of a brazing flux material onto a brazing surface that was simple and allowed the brazing surface with applied flux material to be handled extensively prior to the brazing process. With such a method only the brazing surface and not an entire assembly would have to be fluxed, significantly lessening the capital investment, footprint of the fluxing apparatus, amount of required flux material, and the labor required for the fluxing process.
In one embodiment, the present invention comprises a method for application of a brazing flux material to a brazing surface comprising the steps of: applying a brazing filler material directly onto a substrate by a kinetic spray application to form a brazing surface and subsequently depositing a brazing flux material directly onto the formed brazing surface.
In another embodiment, the present invention comprises a method for application of a brazing flux material to a brazing surface that comprises the steps of: providing a brazing filler material as a particle mixture, entraining the particle mixture into a flow of a gas, the gas at a temperature insufficient to cause thermal softening of the particle mixture, directing the particle mixture entrained in the flow of gas through a supersonic nozzle placed opposite a substrate and accelerating the particle mixture to a velocity sufficient to result in adherence of the particle mixture onto the substrate thereby forming a brazing surface by a kinetic spray application, and then depositing a brazing flux material directly onto the formed brazing surface.